1. Field of the Invention
The present invention relates to a self-foamed porous ceramic composition and a method for making a porous ceramic using the self-foamed porous ceramic composition. More particularly, the present invention relates to a self-foamed porous ceramic composition containing a foamable component capable of generating gas at high temperature, and a method for making a porous ceramic with a high porosity and strength wherein the porous ceramic is made by fabricating the self-foamed porous ceramic composition into a glass, pulverizing the glass into powders, and sintering the glass powder compact to densify and rapidly foam it.
2. Description of the Related Art
Currently used porous ceramics are made by any one of the following processes: i) a process including pre-sintering a ceramic at a temperature not higher than the optimum sintering temperature, ii) a process including mixing a ceramic powder with spherical polymer beads and burning out the polymer beads by heating to form pores therein, and iii) a process including coating a polymer sponge with a ceramic and burning out the polymer sponge to form sponge-type pores, etc.
The pre-sintering process has an advantage that porous ceramics can be easily made, but is disadvantageous in that the porous ceramics have a low strength and their pores have a relatively small size and non-uniform size distribution. Since the process using spherical polymer beads is limited in the amount of the beads added, it is difficult to make porous ceramics having a porosity of 60% or higher. U.S. Pat. No. 3,090,094 (1963) discloses a porous ceramic made using a sponge. The porous ceramic is advantageous in terms of high porosity (60˜90%). However, since the walls defining the pores have a small thickness, the mechanical strength of the porous ceramic is poor. To increase the low mechanical strength, the sponge must be repeatedly coated.
On the other hand, self-foamed porous ceramics are characterized in that they exhibit higher strength with higher porosity than conventional porous ceramics. Currently used self-foamed porous ceramics have been made by mixing a ceramic powder with a polymer foam at room temperature or higher. U.S. Pat. No. 3,833,386 (1974) discloses a porous ceramic made by mixing a ceramic with a polymer foam at room temperature. The porous ceramic exhibits a relatively high strength and its pores have a relatively small pore size of not more than 100 μm, compared to the porous ceramics using sponges. However, the porous ceramic has disadvantages that its pore size and porosity cannot be appropriately controlled and the ceramic content is difficult to control. When a porous ceramic is made using a foamable polymer at high temperature, the polymer is oxidized at high temperature and decomposed into gases such as nitrogen, carbon dioxide, water vapor, etc. which form pores. However, the porous ceramic has disadvantages that its pore size and porosity cannot be appropriately controlled due to difficult control of pore formation, and the strength is low.
Presently known and commercially available porous ceramics are made by the processes discussed above. The problem is that the higher the porosity of the porous ceramics is, the lower the strength is.